The present invention is directed to toners and developer compositions and methods of imaging. More specifically the present invention is directed to toner and developer compositions comprising a combination of charge enhancing additives which is environmentally friendly and has good electrical properties.
Many toner and developer compositions are currently employed in the xerographic art. However, a number of these compositions may pose an environmental hazard, especially to the aquatic environment. Alkyl pyridinium compounds, in particular pure cetyl pyridinium chloride (&gt;99% pure), a component of many toner and developer compositions such as of an aluminum compound of 3,5 dialkyl salicylic acid/CPC containing 7% PV Fast Blue Pigment, 2% an aluminum compound of 3,5 dialkyl salicylic acid, 0.5% cetyl pyridinium chloride and 90.5% styrenebutadiene copolymer and those disclosed in U.S. Pat. Nos. 4,298,672; 5,114,821; 4,752,550 and 5,151,338, may result in undesirable levels in the environment. Such levels are believed to be related to the water extractable alkyl pyridinium level which is the amount of soluble alkyl pyridinium chloride removed from the toner when flushed with water.
Some states of the United States of America, such as California, impose strict regulations on the disposal of materials designated for landfill such as spent xerographic toners. Such materials must pass acute lethal evaluation tests to be classified as non-hazardous. Many current toners containing 2% cetyl pyridinium chloride (CPC) have a LC.sub.50 (lethal concentration to 50% of a population) equal to about 68 mg/1 and may not meet the stringent levels now or soon to be required in some states as well as in some European countries. As a consequence, users of such toner may be confronted with inconvenient and costly waste disposal situations.
Furthermore, positively charged toner compositions having alkyl pyridinium charge enhancing additives are useful in electrostatographic imaging systems such as those which employ a Viton coated fuser roll; however such charge enhancing additives may react with polymers contained on the Viton fuser roll over time causing decomposition of the roll.
One such Viton fuser roll which may be used in electrostatographic copying machines is composed of a soft roll fabricated from lead oxide, du Pont Viton E-430 resin, and vinylidene fluoride hexafluoropropylene copolymer. Excellent image quality has been obtained with such Viton fuser rolls. However, it appears that certain specific charge control additives, such as tetrasubstituted ammonium salts, and alkyl pyridinium compounds, such as cetyl pyridinium chloride, react with the Viton of such Viton fuser rolls. For example, cetyl pyridinium chloride appears to be catalytically decomposed by the lead oxide contained in the fuser roll resulting in a highly unsaturated compound which polymerizes and condenses with the unsaturated Viton E-430 material. As a result, the Viton fuser roll turns black, develops multiple surface cracks, and the surface hardens resulting in image quality deterioration.
Toner compositions comprising the above described charge enhancing additives are useful for causing the development of images formed on layered photoresponsive imaging devices comprised of charge generating and charge transport layers. These devices are charged negatively, rather than positively as is usually the situation with selenium photoreceptors. Thus a toner composition which is positively charged is required in order that the toner particles can be suitably attracted to the electrostatic latent image contained on the photoreceptor surface. In view of this, efforts have been devoted to obtaining developer compositions containing toners which are positively charged. While many charge control additives are known for this purpose, there continues to be a need for new additives. Specifically, there continues to be a need for additives which will not interact with Viton type fuser rolls. Moreover, there continues to be a need for positively charged toner and developer compositions possessing rapid admix charging characteristics. This property allows uncharged toner to rapidly gain charge when introduced into a xerographic developer. Further, there continues to be a need for new charge enhancing additives which can be economically prepared. Additionally, there is a need for substantially non-toxic charge enhancing additives, and a need for charge enhancing additives which can be easily and permanently dispersed in toner resin particles. Also, there is a need for toner compositions with charge stability which can be desirably obtained by extrusion toner processing.
Attempts have been made to remedy such problems by employing toner compositions without alkyl pyridinium compounds such as toner and developer compositions containing mixtures of dimethyl distearyl ammonium methyl sulfate and dimethyl distearyl ammonium bisulfate and as described in U.S. Pat. No. 4,560,635; however sacrificing the advantages of employing alkyl pyridinium compounds. Alkyl pyridinium compounds provide for toners which have conductivities which remain at acceptable levels of greater than or equal to 10.sup.-12 ohm-cm throughout the life of the toner and over as broad a concentration range as possible, typically about 1-4% by weight. This characteristic is thought to be a unique characteristic of toners which contain alkyl pyridinium compounds, in particular halogenated alkyl pyridinium compounds. This is important since environmental conditions and normal toner variation result in tribo fluctuations and corresponding toner concentration fluctuations in xerographic machines.
There is a need for improved toner and developer compositions having the advantages, but not the disadvantages of toner and developer compositions containing alkyl pyridinium compounds.